Plants with fibrous roots will help with the soil erosion. Here are a few suggestions:
Hearts and Flowers is an excellent choice. Fast, low maintenance, low water requirements and neat appearance. Takes sun or shade. It will grow faster in full sun. False Heather (cuphea) is a good choice. Spanish Shawl (heterocentron elegans) Pretty aggressive but easy to control. Wedelia; Very aggressive and harder to control after complete covererage. Other wise known as Weed ail-ia. Mondo grass is very good but slow coverage. Carpet bugle (Ajuga reptens) slugs and snails love it.
Star Jasmine (trachelospermum) a vine with a sweet smell. Slow growing. Of course, there's always bougainvillea. It will creep over the hillside.
Good luck with your garden!